Capillary zone electrophoresis for the diagnosis of congenital hemoglobinopathies.

by addition of calculated amounts of 200 g/L glucose. Serum glucose concentrations attained by this procedure were controlled by measurement with the Beckman Glucose Analyzer. The sensitivity to glucose (calculated for the range 5–10 mmol/L) in phosphate buffer (pH 7.4) was 10.2 Ϯ 3.3 nA ⅐ L ⅐ mmol Ϫ1 (mean of slopes calculated from each experiment Ϯ SE; Fig. 1A).The sensitivity to glucose after exposure to human serum for 15 h was 3.7 Ϯ 1.7 nA ⅐ L ⅐ mmol Ϫ1. After reexposure to buffer, the sensitivity was 8.3 Ϯ 2.0 nA ⅐ L ⅐ mmol Ϫ1. The mean sensitivities in serum were significantly lower in serum compared with buffer before and after exposure to serum (P Ͻ0.01; one-way ANOVA). The corresponding results obtained with flow cells in which a microporous PTFE membrane was placed between the electrode surface and the YSI membrane are shown in Fig. 1B. Again, the sensitivities for glucose (calculated for 5–10 mmol/L) were similar in PBS before (1.7 Ϯ 0.4 nA ⅐ L ⅐ mmol Ϫ1) and after (1.3 Ϯ 0.3 nA ⅐ L ⅐ mmol Ϫ1) exposure to serum. However , in contrast to the experiment without the PTFE membrane, there was no decrease of sensitivity after exposure to serum (1.8 Ϯ 0.4 nA ⅐ L ⅐ mmol Ϫ1). Statistically significant differences between the sensitivities in serum and in buffer before and after serum exposure could not be detected. Exposure of unmodified glucose electrodes to human serum for 15 h decreased the sensitivity to glucose by 55%. When electrodes were subsequently perfused for 1 h with PBS, the sensitivity was restored almost completely. The decrease of sensitivity in serum was prevented when a microporous PTFE membrane was placed between the enzyme layer and the electrode surface. The observation that a membrane that protects only the platinum anode (and not the outer membrane or the enzyme layer) can prevent the loss of sensitivity clearly speaks against the importance of protein adsorption or enzyme inactivation in the loss of sensitivity. On the other hand, these results allow one to conclude indirectly, and therefore cautiously, that processes at the electrode surface that inhibit the detection of hydrogen peroxide, and that are possibly prevented by the protecting membrane, are more important. This is in accordance with the results from other authors that show that sensitivity to glucose in blood or serum is retained best in electrodes that …